The photostability of different chlorophyll forms in dark grown leaves of wheat

Abstract

Formulae were developed for calculation of the relative amount of different pigment forms of dark grown leaves of wheat, present before and after photoreduction of the protochlorophyllide. Three pigment forms were calculated from in vivo absorption spectra: the photoreducible protochlorophyllide with absorption maximum at 650 nm and the two chlorophyll(ide) forms with absorption maximum at 684 nm and 673 nm, respectively. The formulae were used to study the changes of the pigment forms at repeated photoreduction of the protochlorophyllide, and at a repeated treatment involving photoreduction of the protochlorophyllide followed by partial photo‐decomposition of the chlorophyllide formed.Five consecutive photoreductions and reaccumulations of protochlorophyllide were carried out by high intensity irradiations of one second (red light, 700 W m‐2) given at intervals of 3 h. The results show that the pool size of reaccumulated protochlorophyllide decreased sharply with the number of photoreductions performed. The absorption spectrum of the chlorophyllide formed at each photoreduction proceeded through the Shibata shift (transformation of the 684‐form to the 673‐form) and the late red‐shift (transformation of the 673‐form to other pigment form(s) in the dark).High intensity irradiation for ten minutes (red light, 700 W m‐2) immediately after each phototransformation caused a photodecomposition of about three quarters of the newly formed chlorophyllide (which was in the 684‐form) while the earlier formed chlorophyll(ide) (in the 673‐form) appeared not to be decomposed. This partial photodecomposition of the chlorophyllide had no effect on further accumulation of protochlorophyllide in the dark, and the absorption spectrum of the remaining chlorophyllide proceeded through the Shibata shift. The partial photodecomposition caused an inhibition of the late red‐shift, and the accumulated chlorophyll(ide) remained in the 673‐form.